[sdiy] Anyone built the ELEKTOR VOCODER?

[Scott Bernardi]

Before anybody tries to build my design, let me mention this caveat! The
circuit looks good on paper, but when I breadboarded a couple of stages
I found the filters and WAY to sensitive to component tolerance! All
those calculations I did to find the nearest 5% resistance just WILL NOT
work. The multiple feedback bandpass filter design requires around 0.1%
tolerance. All the parameters are interactive - Fc, Q, and gain, so if
you want to use trimpots its a real pain to trim.
I picked up Don Lancaster's Active Filter Cookbook to delve into the
theory more, and came to the conclusion that I needed state variable
filters.
These can be tuned nicely, but the parts count increases dramatically (3
opamps per filter stage). I was even looking into doing third order
filters (3 cascaded state variables) and whereas it looks like it would
work quite nicely (I've done some computer simulations), we're talking
about 100's of opamps here. 
I am debating whether I even want to even tackle building a vocoder. I
mean, you can get a WarpFactory by Electrix (24 band DSP vocoder) for
under $300 on ebay nowadays (there's two listed right now). I'd be
spending near that just for parts on a 14 band analog vocoder.

Kevin Peek wrote:
> 
> Just wondering if anyone has built the ELEKTOR Vocoder before?
> 
> I downloaded the files from : http://omega.tellus.vallentuna.se/anders/
> 
> It looks rather more complicated than what I had in mind. I was
> wanting to build something like Scott Bernardi's design.
> But I am willing to try the ELEKTOR if it not too difficult.
> 
> Thanks.
> Kevin

-- 
Scott Bernardi
sbernardi at home.net